Vanadium redox flow batteries are among the most promising technologies for large-scale energy storage, offering high safety, scalability, and stable performance through an aqueous electrolyte system. These attributes enable efficient integration of intermittent renewable sources such as wind and solar power. However, widespread deployment is constrained by limitations at the negative electrode, where the V3+/V2+ redox couple exhibits sluggish kinetics compared to the V5+/V4+ reaction at the positive electrode. Graphite felt, the most commonly used electrode material, satisfies several desirable properties: high conductivity, chemical stability, and large surface area; but suffers poor electrochemical activity toward V3+/V2+ conversion. This mismatch in reaction rates, combined with parasitic hydrogen evolution within the operating potential window and polarization losses, significantly reduces overall battery efficiency. This review critically examines strategies to overcome these challenges, including the role of functional groups on the electrode surface, electrocatalyst incorporation, and alternative electrode materials. The discussion begins with an analysis of fundamental limitations, side reactions, and degradation mechanisms, followed by criteria for electrode selection and the role of surface functional groups in enhancing kinetics. Approaches for electrocatalyst design and their impact on reaction rates are highlighted, and future research directions are proposed to accelerate the development of such batteries. By addressing the bottleneck at the negative electrode, these advancements aim to improve energy efficiency and durability, paving the way for broader adoption of such redox flow battery technology in grid-scale applications.
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